Borehole gravimetry has now been developed into a reasonably reliable tool for oil well logging. Borehole gravimetric techniques provide an indication of the bulk density of formation rock surrounding the borehole being logged. Gravimetric logging services now commercially available include that provided by Exploration Data Consultants (EDCON) of Denver, Co., using a gravity meter of the type developed by LaCoste and Romberg. If accurate measurements of porosity of the formation rock are available, the residual oil saturation can be calculated to a high degree of accuracy. One such application of borehole gravimetry logging in the determination of residual oil saturation in a subsurface formation is set forth in U.S. Pat. No. 4,399,693 to L. S. Gournay.